1. Field of the Invention
This invention relates to devices which can be used for efficiently transferring pressure energy contained in one fluid under pressure to a second fluid at a lower pressure, so that the pressure of the first fluid is relieved and the pressure of the second fluid is increased with a minimal energy loss. More particularly, the present invention relates to an energy exchange engine which includes a rotor which alternately and sequentially, by rotation, places fluid passageways in the rotor thereof in alternating communication with sources of relatively high and relatively low pressure fluids conveyed to fluid passageways in the rotor through ported stator blocks disposed at opposite ends of the rotor.
2. Brief Description of the Prior Art
In some industrial processes, elevated fluid pressures are required only in certain parts of the operation to achieve desired results, following which the pressurized fluid is depressurized. In other processes, some fluids used in the process are available at high pressures and others at low pressures, and it is desirable to exchange pressure energy between those two fluids. In some applications, great improvement in economy of operation can be effected if pressure energy can be efficiently transferred between two liquids or between pumpable slurries of liquid-solid mixtures. A process of this type is the exchange crystallization or melting point inversion process of effecting desalination of sea water or brackish waters. A procedure of this type is that which is described in U.S. Pat. No. 3,431,747.
In the exchange crystallization process, a slurry of ice and hydrocarbon is placed under super-atmospheric pressure in order to reserve the order of freezing so that the ice crystals melt and the hydrocarbon is partially frozen. After this, the water derived from melting the ice is separated from the hydrocarbon, which is in the form of a slurry of solid hydrocarbon particles with the liquid hydrocarbon, and the separated phases are then depressurized to near atmospheric pressure. The procedure is operated cyclically and the economy with which the exchange crystallization-desalination process can be protected is directly dependent upon the efficiency with which the energy input to the process upon pressurization of the ice-hydrocarbon system can be recovered after separation of the water from the hydrocarbon and upon subsequent depressurization of the separated phases.
In U.S. Pat. No. 3,431,747 issued to Hadi T. Hashemi and Jerry L. Lott on Mar. 11, 1969, there is described a device or apparatus which permits pressure energy to be exchanged between relatively high and relatively low pressure fluid systems, and particularly, between liquids or between liquids and slurries which are at two different pressures. The apparatus permits a high percentage of the total energy of the pressurized liquid to be transferred to a liquid at lower pressure.
The apparatus described in U.S. Pat. No. 3,431,747 comprises a rotor assembly which moves during rotation against a stationary structure. The rotor assembly includes a cylindrical rotor body having a plurality of substantially parallel bores extending longitudinally of the body from one end thereof to the other. A freely movable separatory member is positioned in each of the bores and is movable along the bore and dimensioned to divide the bore into a pair of chambers. The cylindrical rotor body utilized in the described apparatus has a pair of opposed planar, substantially parallel end faces at which the bores through the rotor open in radially spaced, equidistant relation from a central rotational axis of the rotor.
The cylindrical rotor body is mounted in a surrounding rotor housing which is closed at its opposite ends by a pair of closure plates which receive a central shaft affixed to opposite end faces of the rotor, and which journal the shaft for rotational mounting of the rotor. Radially displaced in each of the closure plates from the projected axis of rotation of the rotor are a plurality of fluid passageways extending through the respective closure plates and communicating with bores formed through a seal plate interposed between each of the respective closure plates and a respective end face of the rotor. The seal plates are keyed to the adjacent closure plates and bear sealingly against the planar end faces of the rotor in a manner to facilitate intermittent and periodic communication between the ports formed through the seal plates and the elongated, parallel bores extending longitudinally through the rotor body.
In operation, a source of high pressure fluid is connected to one or more of the fluid passageways through one of the closure plates, and a source of low pressure fluid is connected to one or more of the other of the fluid passageways through the same closure plate. In the same way, a high pressure fluid source is connected to one or more passageways in the second closure plate located at the opposite end of the rotor assembly, and a low pressure fluid source is connected to one or more of the other fluid passageways therethrough. From the described structural relationship of the closure plates, seal plates and rotor, and more particularly, of the intermittent communication between the bores of the rotor and aligned ports through the seal plates, and the fluid passageways through the closure plates, it will be perceived that at such time as one of the rotor bores is aligned with a port in the seal plate, it receives or discharges either high or low pressure fluid, respectively, which acts upon the freely movable separatory member disposed in the respective bore. At the same time, the same bore through the rotor is aligned with a port in the seal plate at the other end of the rotor body, which port is, of course, in communication with one of the fluid passageways through the closure plate at that end of the assembly. There will thus be an introduction of fluid to the same bore in the rotor from the opposite end thereof so as to act upon the separatory member in that bore on the opposite side thereof from the side upon which fluid entering the bore from the opposite end of the rotor body acts.
By appropriately synchronizing the intermittent and periodic communications between each rotor bore with sources of high and low pressure as effected through the interpositioned seal plate ports and closure plate fluid passageways, the pressure energy can be caused to transfer via the movable separatory member in each of the bores in such a way as to increase the pressure of the relatively low pressure fluid in one end of the bore, while relieving and decreasing the pressure of the high pressure fluid in the other end of the bore.
Ease of displacement of the separatory member is characteristic of the structure, and the transfer of pressure energy is highly efficient due to the minimum energy requirement to displace these elements in their respective bores. Moreover, the system does not employ conventional valving which can become choked or clogged by any entrained material carried in liquids, or even by slurries when they are employed as the fluids between which the pressure energy is to be transferred.
Subsequent to the patenting of the energy exchange engine as illustrated and described in U.S. Pat. No. 3,431,747, improvements have been made in the type of seal plate structure employed in such pressure energy transfer devices. The need for such improvement has arisen largely out of the difficulty of providing efficient and smoothly functioning seal members between the moving rotor structure and the closure plates provided at opposite ends thereof, where such seal members are utilized for periodically and intermittently communicating high and low pressure fluids, in alternating sequence, to the bores of the rotor. It will be apparent that the nature of this periodic and intermittent communication is such that a bore opening moves rapidly into and out of communication with a registering port or fluid passageway formed in the stationary closure plate or stator block at the end of the rotor assembly, and it is necessary to nearly instantaneously establish communication to facilitate fluid flow into the rotor bore, and then nearly instantaneously terminate such communication without loss of fluid between the contacting planar surfaces.
The problem of maintaining an effective seal prior to and immediately following the establishment of communication in the manner described is compounded by the fact that relatively high and relatively low pressure fluids are alternately being passed into and out of the same bore in the rotor to different ports or fluid passageways in the closure plate as the fluid in one end of each bore is alternately introduced at high pressure and then, following decompression, is discharged at a relatively low pressure in response to the entry of a higher pressure fluid into the opposite end of the bore. Stated differently, any sealing structure which is interposed between the planar end face of the moving rotor and the stationary closure plate or stator block through which fluids are communicated with the rotor is necessarily subjected to fluctuating forces during each cycle of the rotor as the ports through the sealing structure, and serving to establish communication between the rotor bores and the fluid passageways in the closure plates, are used for alternately passing high pressure fluid and then low pressure fluid.
Improvements in the seal plate structures utilized in pressure energy exchange apparatus of the type described have taken the form of disk-shaped seal plates which are provided with ports of varying area, size and geometry, and with certain relieved areas formed in the opposite planar faces of such seal plates at locations between the ports. Structures of this type which have effected a significant improvement in the sealing function in these types of energy exchange engines are depicted and described in U.S. Pat. Nos. 3,582,090 and 3,910,587. In each of these patented structures, however, it has still been thought necessary to retain, as a portion of the seal plate structures there described and illustrated, many O-ring seal rings around the various ports which are provided and, due to the somewhat asymmetric geometry of some of the port shapes, the configurations of such sealing rings have, of necessity, also been asymmetrical. The seal plates which have heretofore been proposed have, moreover, functioned more efficiently, and with less frictional drag imposed on the system, at certain rotational speeds of the rotor and line pressures of the system than at others as the pressure exchange apparatus is utilized under varying conditions. It has thus been necessary to design the seal plates for effecting sealing at that time during the rotational cycle of the rotor when the most severe operating conditions are encountered. In doing so, the result has been that a relatively higher frictional drag is imposed on the system, and a higher rate of seal plate wear occurs, at certain times during the rotational cycle of the rotor, as compared to other times when the seal plates are called upon to effect sealing under pressure conditions which more nearly balance the fluid forces acting on opposite sides of the seal plates.